1. Field of the Invention
The invention relates to a drive circuit with an external mode-adjusting pin, and more particularly to the drive circuit with an external mode-adjusting pin that implements an external pin for selecting either a resistor or a capacitor to determine the operational mode of a driven circuit.
2. Description of the Prior Art
Referring now to FIG. 1, a conventional operational element integrated circuit is illustrated. As shown, this conventional operational element integrated circuit PA1 includes a driven circuit PA11 and a drive circuit PA12, in which the driven circuit PA11 is particularly an LED circuit further having a power source PA111, a full wave bridge rectifier circuit PA112, a resistor PA113, a diode PA114, a capacitor PA115, at least one operational element PA116 (LED herein), an inductor PA117, a first switch PA118, a resistor PA119 and two capacitors PA120, PA121.
The full wave bridge rectifier circuit PA112 is coupled with the power source PA111, and also couples the resistor PA113, the diode PA114, the capacitor PA115 and the operational element PA116. One end of the inductor PA117 is coupled with the diode PA114 and a drain of the first switch PA118, while another end thereof is coupled with the capacitor PA115 and the operational element PA116. The resistor PA119 is coupled with a source of the first switch PA118, and also couples a CS port of the drive circuit PA12. The capacitor PA120 is coupled with the resistor PA113, and also couples a VCC port of the drive circuit PA12. The capacitor PA121 is coupled with a COMP port of the drive circuit PA12. The first switch PA118 is coupled with an OUT port of the drive circuit PA12.
In this conventional operational element integrated circuit, as the first switch PA118 is ON, the inductor PA117 would generate a induced current. Generally speaking, the operational mode of the driven circuit PA11 is determined by the ON time of the first switch PA118 (for controlling up and down of the induced current). Further, major operational modes include a continuous conduction mode (CCM), a discontinuous conduction mode (DCM) and a boundary conduction mode (BCM). In addition, the operational mode is specified by the charge/discharge of the induced current.
Nevertheless, the aforesaid operational modes may exist different merits and shortcomings. In practical usage in the art, for the conventional driven circuit PA11 is limited to the specific circuit structuring, thus it is usual that only one single operational mode is applied in consideration of the efficiency, electromagnetic interference and costing. Obviously, as soon as a specific operational mode is chosen in the initial application, then all the follow-up applications of this current circuit would be inevitably to apply the same old operational mode, even though another operational mode may be much more appropriate. Hence, the embedded inconvenience therefrom is apparent.